The invention is generally directed to the field of disc drives and more particularly to controlling acoustic noise emissions emanating from a disc drive voice coil motor assembly while maintaining a sealed environment for the internal components of a disc drive.
Modern disc drives comprise one or more discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks. Data is typically written to, and read from, the tracks via transducers (xe2x80x9cheadsxe2x80x9d) typically mounted to a radial actuator assembly, which positions the heads relative to the discs. Various disc drive components, including the spindle motor and the actuator assembly, are fastened to a base plate. A top cover is attached to the base plate and sealed with a pressure seal to enclose and create a sealed environment for the disc drive components. This sealed environment reduces the chance that outside contaminants, such as dust, will interfere with read/write operations of the actuator assembly, among other things.
Radial actuator assemblies employ a voice coil motor (VCM) to position the heads with respect to the disc surfaces. The heads are mounted via flexures at the ends of a plurality of actuator arms, which project radially outward from a substantially cylindrical actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Normally, the VCM includes a coil mounted on the side of the actuator body opposite the actuator arms between an array of permanent magnets which are positioned above and/or below the coil on top and/or bottom magnet plates or poles, respectively. When controlled current is passed through the coil, an electromagnetic field is generated. The generated electromagnetic field interacts with the magnetic field of the permanent magnets thus causing the coil to move relative to the magnets in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads are moved across the disc surfaces.
Typically, the heads are supported on the actuator arms in a position over the discs by actuator slider assemblies, which include air-bearing surfaces designed to interact with a thin layer of moving air generated by the rotation of the discs, so that the heads xe2x80x9cflyxe2x80x9d over the disc surfaces. Generally, the heads write data to a selected data track on the disc surface by selectively magnetizing portions of the data track through the application of a time-varying write current to the head. In order to subsequently read back the data stored on the data track, the head detects flux transitions in the magnetic fields on the data track and converts these flux transitions to a signal which is decoded by read channel circuitry of the disc drive.
A closed-loop servo system is typically used to control the position of the heads with respect to the disc surfaces. More particularly, during a track following mode in which a head is caused to follow a selected data track, servo information is read which provides a position error signal indicative of the position of the head relative to a center line of the track. The position error signal is used, when necessary, to generate a correction signal that in turn is provided to a power amplifier. The power amplifier then passes current through the actuator coil to adjust the position of the head relative to the track.
During a seek operation, the servo system receives the address of the destination track and generates control signals that cause the heads to initially accelerate and then subsequently decelerate as the head nears the destination track. At some point towards the end of the deceleration of the head, the servo system will transition to a settle mode during which the head is settled onto the destination track and, thereafter, the servo system causes the head to follow the destination track in a track following mode.
A general trend in the disc drive industry is to reduce the level of acoustic emissions or noise generated by disc drives, preferably reducing the noise to a level that is below the human hearing threshold. There are two primary sources of acoustic emissions or noise in disc drives: idle noise and seek noise. Idle noise results from the operation of the spindle motor and its associated rotating discs. Significant improvements in reducing idle noise have been achieved by replacing ball bearing assemblies with hydraulic bearings in the spindle motor. In contrast, seek noise results from vibrations in the permanent magnets and/or poles of the VCM caused when current is passed through the VCM coil. The vibrations occurring in the poles of the voice coil motor may be transmitted to the top cover and/or the disc drive base plate either as sympathetic vibrations or as direct transmissions.
Another trend in the disc drive industry is to reduce the weight of the disc drives for use in the lap top computers and other equipment that requires portability. Thus the designers of disk drives are faced with the task of reducing their weight while not sacrificing their robustness. One way to reduce the weight is by reducing the thickness of various components. Such reduction in thickness invariably reduces the stiffness of the parts. The decrease in weight of disc drives may cause problems with the integrity of the pressure seal between the top cover and the base plate because thinner top covers are more easily deformed.
One approach to reducing the seek noise from the disc drive has been to slow down the seek operation. A slowed down seek operational setting, called a quite seek, is often provided in disc drives as an optional setting. The alternative operational setting in disc drives having a quite seek setting is an operational setting commonly referred to as the performance seek, where the seek to the track occurs quickly relative to the quite seek. However, while the quite seek reduces the acoustical emissions from the disc drive, it also necessarily reduces disc drive performance. Disc drives including such quite seek operational settings are often employed in areas, such as government and private offices, that are subject to strict environmental noise limitations.
Another approach to reducing the acoustical emissions from the disc drive is to add a damping material between the upper magnetic plate or top pole and the top cover of the disc drive. For this approach to be effective, the top cover must be sufficiently rigid to provide deflection of the damping material. However, the stiffness required for this approach to be useful may add unacceptable weight and manufacturing costs to the disc drive. Further, if the cover is not sufficiently stiff, the addition of damping material between the cover and the top pole may cause the top cover to deform and breach the pressure seal between the cover and the base plate. Breach of this pressure seal allows contaminants into the disc drive and thus, may prevent the disc drive from operating effectively.
In addition to adversely affecting the integrity of the pressure seal, adding a damper between the top pole and the top cover may add significant costs to the manufacturing of the disc drive.
Accordingly there is a need for a damping system and/or method which effectively reduces VCM vibrations in a disc drive and, thereby, reduces acoustical emissions while at the same time does not adversely affect the integrity of the disc drive pressure seal or add significant costs to the manufacture of the disc drive.
Against this backdrop various embodiments of the present invention have been developed. In general, the various embodiments of the present invention relate to systems and methods of minimizing vibrationally induced noise in a disc drive servo system. Additionally, embodiments of the present invention relate to reducing vibrationally induced acoustical emissions from a disc drive device.
A disc drive has a base plate, a voice coil motor operably attached to the base plate, and a top cover attached to the base plate with two perimeter fasteners and one interior fastener through corresponding apertures in the top cover. The two perimeter fasteners/apertures and the interior fastener/aperture form a triangular portion of the top cover that has increased stiffness and rigidity due to the proximity of the fasteners to each other. A pressure seal is positioned between the top cover and the base plate to seal the disc drive to form an internal sealed environment for the various disc drive components. An acoustic damper is positioned between and contacts the voice coil motor and the triangular portion of the top cover to dampen vibrations occurring in the voice coil motor and the top cover. The acoustic damper is made of the same material as the pressure seal.
In another embodiment, a second acoustic damper is positioned between the base plate and the voice coil motor such that it does not contact the top cover. The second acoustic damper need not to be positioned within the triangle formed by the two perimeter fasteners and the interior fastener.
The voice coil motor includes a bottom pole attached to the base plate, a top pole operably connected to the bottom pole in a manner such that the top pole is maintained in a spaced relationship to the bottom pole, and a single magnet pair positioned between the top pole and the bottom pole. The first acoustic damper is preferably positioned between the top pole and the top cover and the second acoustic damper is preferably positioned between the bottom pole and the bottom cover.
In yet another embodiment of the present invention, a stiffening ridge is added to the top cover to create an isolated portion of the top cover over the top pole of the voice coil motor; the isolated portion is stiffer and more rigid than the remainder of the top cover. The isolated portion may be outside of the triangular portion, may partially overlap the triangular portion, or may be contained entirely within the triangular portion. The acoustic damper may be positioned between the isolated portion and the voice coil motor to dampen acoustic noise without adversely affecting the integrity of the pressure seal.
The disc drive is manufactured by operably attaching the voice coil motor to the base plate and then attaching the top cover to the base plate using at least the two perimeter fasteners and the interior fastener. A pressure seal is positioned between and contacts the top cover and the base plate and an acoustic damper is positioned between and contacts the voice coil motor and the triangular portion of the top cover. The pressure seal and acoustic damper may be applied to the top cover prior to attaching the cover to the base plate or applied to the base plate and the voice coil motor, respectively prior to attaching the cover to the base plate. The same process is preferably used to apply the acoustic damper as to position the pressure seal which adds little or no additional cost to the manufacture of the disc drive.
These and various other features as well as advantages which characterize the various embodiments of the present invention will be apparent from a reading of the following detailed description, a review of the associated drawings, and the appended claims.